R: Summary of a Survival Curve

summary.survfit {survival}

R Documentation

Summary of a Survival Curve

Description

Returns a list containing the survival curve, confidence limits for the curve, and other information.

Usage

  ## S3 method for class 'survfit'
summary(object, times, censored=FALSE, scale=1,
  extend=FALSE, rmean=getOption('survfit.rmean'), data.frame=FALSE, dosum, ...)
  ## S3 method for class 'survfitms'
summary(object, times, censored=FALSE, scale=1,
  extend=FALSE, rmean=getOption('survfit.rmean'), data.frame=FALSE, ...)

Arguments

`object`	the result of a call to the `survfit` function.
`times`	vector of times; the returned matrix will contain 1 row for each time. The vector will be sorted into increasing order; missing values are not allowed. If `censored=T`, the default `times` vector contains all the unique times in `fit`, otherwise the default `times` vector uses only the event (death) times.
`censored`	logical value: should the censoring times be included in the output? This is ignored if the `times` argument is present.
`scale`	numeric value to rescale the survival time, e.g., if the input data to `survfit` were in days, `scale = 365.25` would scale the output to years.
`extend`	logical value: if TRUE, prints information for all specified `times`, even if there are no subjects left at the end of the specified `times`. This is only used if the `times` argument is present.
`rmean`	Show restricted mean: see `print.survfit` for details
`data.frame`	if TRUE, return the results as a data frame, rather than a summary.survfit object
`dosum`	only applicable if `times` is present, see details below
`...`	for future methods

Value

if data.frame = TRUE, a data frame with columns of time, n.risk, n.event, n.censor, surv, cumhaz, strata (if present) and data (the row of newdata for survfit.coxph). Also std.err, std.chaz, upper and lower if the curve had se.fit=TRUE.

if data.frame = FALSE, a list with the following components:

`surv`	the estimate of survival at time t+0.
`time`	the timepoints on the curve.
`n.risk`	the number of subjects at risk at time t-0 (but see the comments on weights in the `survfit` help file).
`n.event`	if the `times` argument is missing, then this column is the number of events that occurred at time t. Otherwise, it is the cumulative number of events that have occurred since the last time listed until time t+0.
`n.entered`	This is present only for counting process survival data. If the `times` argument is missing, this column is the number of subjects that entered at time t. Otherwise, it is the cumulative number of subjects that have entered since the last time listed until time t.
`n.exit.censored`	if the `times` argument is missing, this column is the number of subjects that left without an event at time t. Otherwise, it is the cumulative number of subjects that have left without an event since the last time listed until time t+0. This is only present for counting process survival data.
`std.err`	the standard error of the survival value.
`conf.int`	level of confidence for the confidence intervals of survival.
`lower`	lower confidence limits for the curve.
`upper`	upper confidence limits for the curve.
`strata`	indicates stratification of curve estimation. If `strata` is not `NULL`, there are multiple curves in the result and the `surv`, `time`, `n.risk`, etc. vectors will contain multiple curves, pasted end to end. The levels of `strata` (a factor) are the labels for the curves.
`call`	the statement used to create the `fit` object.
`na.action`	same as for `fit`, if present.
`table`	table of information that is returned from `print.survfit` function.
`type`	type of data censoring. Passed through from the fit object.

Details

This routine has two uses: printing out a survival curve at specified time points (often yearly), or extracting the values at specified time points for further processing. In the first case we normally want extend=FALSE, i.e., don't print out data past the end of the curve. If the times option only contains values beyond the last point in the curve then there is nothing to print and an error message will result. For the second usage we often want extend=TRUE, so that the results will have a predictable length. If data.frame = TRUE then either might be desired. Be aware, however, that these extended values will often be badly biased; we are essentialy treating the final censored subjects as immortal.

The underlying survival object will have a row for each unique event or censoring time. When the times argument contains values not in the data, the routine can only use a best guess for the number at risk, i.e., the number at risk at the next event/censoring time. When the routine is called with counting process data many users are confused by counts that appear too large. For example, Surv(c(0,0, 1, 5), c(2, 3, 8, 10), c(1, 0, 1, 0)), which prints as (0,2] (0, 3+] (1, 8] (5,10+]. Do survfit followed by summary with a request for the values at time 0. The survfit object has entries only at times 2, 3, 8, and 10; there are 3 subjects at risk at time 2, so that is what will be printed for time 0.

For a printout at fixed times, for example yearly values for a curve, the printed number of events will by default be the total number of events that have occured since the prior line of printout, and likewise for number of censored and number at entry, dosum = TRUE. Alternately, the routine can return the number of events/censors/entry at that time, dosum=FALSE. This feature was added at the request of a user who essentially wanted to use the times argument as a subscript to pick off selected rows of the output, e.g., to select survival values corresponding to the last follow-up times of a new set of observations. The default for dosum is TRUE if the times vector is strictly increasing and FALSE otherwise.

For a survfitms object replace the surv component with pstate. Also, a data frame will not include the cumulative hazard since it has a different multiplicity: one column per transition rather than one per state.

Examples

summary( survfit( Surv(futime, fustat)~1, data=ovarian))
summary( survfit( Surv(futime, fustat)~rx, data=ovarian))

[Package survival version 3.8-3 Index]